1. Field of the Invention
The present invention relates to a lower inertial compact disk driving device, and particularly to a lower inertial compact disk driving device, wherein an optical unit device is used as a medium of the laser beam and a displacing device is used to change the position of the optical unit device, thereby, light spots are located on a focusing device of a disk precisely.
2. Description of the Prior Art
In the current compact disk driving device, the disk rotates and the laser head make a straight and reciprocal movement. The prior technic lower speed compact disk drive uses a constant linear velocity (CLV) or constant angular velocity (CAV). The laser head has the constant speed as reading data. Another conventional way is used to increase the reading speed by increasing the rotation speed. Some current compact disk drive and DVD ROM use xe2x80x9cTrue Xxe2x80x9d multi-beam technology, which is used to assure the reading in the whole disk has the same speed. The speed changes only when the mass of the compact disk and the operation system are different.
The technologies for reading DVD are not the same in different kinds of compact disk drives. In the prior art, to be compatible with the common CD ROM, the DVD ROM use two heads technology to real the auto adjustment of the servo unit device of a compact disk driving device so that the accuracy of reading data is improved. Double dynamic shock suspending (DDSS) system is used to effectively reduce the shock as a compact disk drive rotates with a high speed. Auto balance system (ABS) is used to retain the disk to be horizontal so that the reading ability of the compact disk is improved. Automatic intelligent error correction is used so that the reading amount of a disk is improved greatly. The above said many technologies cause the performance of a compact disk driving drive to be improved. However, current compact disk driving device uses a high rotation speed disk and a laser head of straight and reciprocal movement. The inertial of the disk is too large and the mass of the laser head is large. Therefore, the current used compact disk driving device consumes much power and has a large shock so that the moving range of the disk is confined. For example the current compact disk drive cannot be used in a personal digital assistant (PDA), which has the function of calculation, phone, facsimile, network, etc. These functions can be realized wirelessly. The extra equipment of PDA consumes low power. However, current compact disk drive has a large rotation inertia and the laser head is heavy and thus can not realize the object of lower power consumption.
Moreover, disks are data density, possible achieving to a value of 108 bit/cm2, accordingly, the disk has a small track interval and bit area. The current track interval for CD-ROM is 1.6 xcexcm with a least bit length of 0.83 xcexcm. The track interval for DVD is 0.84 xcexcm with a least bit length of 0.45 xcexcm. To read data precisely, the components of a compact disk drive must have a precision of sub-micron. In general, the reading compact point and the axial shift of a signal-storing plane cannot be over xc2x11 xcexcm. If this is only achieved by mechanical system, then the system must have a precision of sub-micron, and is work at the same precision, This is almost impossible.
The current compact disk drive uses a servo system for assuring the precision of positioning of a compact disk drive. The servo system is a basic servo system of a compact disk drive. The laser beam can be accurately positioned on a recording surface of a disk so that the optical spot may rotate and shift with the disk and tracks the recording surface automatically. Conventionally, there are many ways for detecting the focusing error of a laser head, such as detect method using beam of light deviated the center of field lens; detect method by refraction of cylindrical lens, detect method by critical angle, etc. In holographic lens, the reading of data and servo signal are performed by holographic elements. The methods for detecting signals are such as spot size detection (SSD). However, current focusing device will perform a straight and reciprocal movement repeatedly as it is installed on a laser head. Since the focus coil is heavy, the straight and reciprocal movement will cause a large instantaneous speed and thus a large electric power is consumed.
Accordingly, the primary object of the present invention is to provide a lower inertial compact disk driving device wherein in operation, the laser head and the disk are static. A displacing device is used to change the position of the laser beam incident upon a disk. The displacing device has a rotary needle, a rotation-driving device and a displacing device. The rotary needle is installed below the lower side of a written surface of the disk. A center of the rotary needle is installed with a fixed reflector, and selected positions at two sides thereof are installed with a movable reflector and a balance block, respectively. The rotation-driving device is used to control the rotation of the rotary needle and the displacing device is used to control the opposite movement of the balance block and the rotary needle so as to control the change of a data reading optical path.
Another object of the present invention is to provide a lower inertial compact disk driving device, wherein the focus of the laser beam from the laser head is precisely located at the optical recording surface. The light spots tracks the movement of the recording surface so that the recording surface is retained in a range of the focus.
A further object of the present invention is to provide a lower inertial compact disk driving device, wherein a close loop focus control loop is used, and light spot detect method is used to detect servo signal. The focusing servo signal is phase and amplitude compensated and then is amplified so as to drive a focusing device to control the movement of a focusing lens and thus light spots are radiated to a disk precisely.